The present invention relates to a curable polyurethane resin composition and a casting tape for surgery prepared by using the same. More particularly, the invention relates to a moisture-curable polyurethane resin composition having improved storage stability and suitable as an adhesive, sealant and coating composition as well as for use in the preparation of a casting tape for surgery.
As is well known, polyurethane resin compositions are used in a very wide field of applications in the preparation of, for example, coating compositions, sealants, adhesives, artificial leathers, resin rollers and the like. Curable polyurethane resin compositions are supplied either in the form of a one-package product, which is a blend of all of the necessary ingredients and curable when exposed to a moisture-containing atmosphere, or in the form of a two-package product, which is supplied in two packages each containing different ingredients to be blended together immediately before use so as to start the curing reaction. The one-package type polyurethane resin compositions are preferred to the two-package type products because of the easiness in handling not requiring exact weighing and mixing of the contents of the two packages before use to be freed from the troubles due to errors in weighing and incomplete mixing not to obtain full and even exhibition of the properties of the cured resin composition. In particular, casting tapes used as a plaster bandage in surgery are prepared by using a moisture-curable polyurethane resin composition of the one-package type.
Namely, traditional plaster bandages prepared by impregnating a loosely woven cloth such as gauze with calcined gypsum are under continuous replacement with a polyurethane resin-based casting tape prepared by impregnating a flexible substrate such as a glass fiber cloth with a moisture-curable polyurethane resin composition having a pasty consistency. Such a polyurethane resin-based surgical casting tape is stored under a hermetically sealed condition and, when the casting tape is taken out and wound around the affected part of the patient, curing reaction of the polyurethane resin composition proceeds by contacting with water or moisture in the air.
Various types of moisture-curable polyurethane resin compositions have been proposed for use in the preparation of the above described surgical casting tapes including those polyurethane prepolymers consisting of an aromatic polyisocyanate and a polyol disclosed, for example, in Japanese Patent Kokai 54-100181 and elsewhere.
While it is usual that a moisture-curable polyurethane resin composition is admixed with a catalyst to promote the curing reaction of the resin composition when it is contacted with moisture, a problem in the use of a curing catalyst is that the storage stability of the polyurethane resin composition is decreased thereby to cause premature curing or gelation of the composition during storage so that it is also usual to compound the moisture-curable polyurethane resin composition with a stabilizer. Accordingly, a proper choice of the combination of a curing catalyst and a stabilizer is very important in a moisture-curable polyurethane resin composition and a surgical casting tape prepared therewith. For example, U.S. Pat. No. 4,433,680 proposes dimorpholino diethyl ether as the curing catalyst and benzoyl chloride as the stabilizer and U.S. Pat. No. 4,574,793 proposes bis(2,6-dimethylmorpholino) diethyl ether as the curing catalyst and methane sulfonic acid as the stabilizer. These prior art formulations, however, are not always quite satisfactory in respect of the balance of the curability and the stabilizing effect because satisfactory storage stability can hardly be obtained without affecting the curability of the composition. Thus, it is eagerly desired to develop a moisture-curable polyurethane resin composition having excellent storage stability without substantially affecting the curability of the composition.